A man may be trapped inside the rubble of a disused pub that collapsed after an explosion on Sunday.
Firefighters have been trying to get into the former Old Locomotive pub in Canterbury, Kent after reports that a man may have been inside.
They were initially pulled back because of the further risk of collapse but they are now beginning to sift through the rubble.
Another man, believed to be the former landlord, was slightly injured in the blast, which is thought to have been caused by a ruptured gas main.
It is thought that the trapped man may have been a squatter.
A Fire Brigade spokesman said: "It has been derelict for two years but it is known that there has been a squatter presence in the premises during that time.
"I don't know whether it was the landlord that said there was someone in there or whether it was one of the neighbours."
Fire crews were dousing flames caused by the explosion at 2130 BST when the building in Station Road West collapsed.
Firefighter Brian Wash told BBC Kent that early indications were that someone was in the building at the time of the explosion.
He had been forced to pull firefighters back because of the risk of further collapse.
Mr Wash said: "The buildings on either side in some way cushioned the blast.
"Normally you would expect some lateral movement, but the building took the full brunt of the blast and it's literally come down like a deck of cards into its own cellar."
A Kent Police spokesman said: "There is someone unaccounted for, but we don't know if he was in there at the time."
Fire crews will be using a snake-eye camera and a vibraphone - equipment used to search for people trapped after an earthquake.
The search is expected to last most of the day.